Paul Williams, Oscar-winning songwriter and ’70s icon who faded into obscurity, showed signs of a comeback after the premiere of a new film about his life, “Paul Williams: Still Alive.” After a screening at HBO, the tunesmith, who wrote the Carpenters’ “We’ve Only Just Begun,” hit jazz club Iridium, where he played the title track from the doc, with ex-Wings guitarist Laurence Juber. The ditty will be pushed as an Oscar contender for Best Original Song. Also at the Creative Coalition event were director Stephen Kessler and songwriter Kenneth Ascher.